Gas plasma treatment of a variety of substrates, particularly those in the electronics field, is a well-established and proven process that increases surface activation (wettability), improves die attach, increases the reliability and strength of wire bonds, and provides better adhesion for encapsulation. Plasma systems have been in use for over 25 years for such applications and offer significant advantages over liquid chemical treatment methods and other dry methods such as ozone.
Disclosed in U.S. Pat. No. 4,208,159, issued to Uehara et al. on Jun. 17, 1980, is an apparatus that performs, in an automated assembly line manner, the plasma treatment of individual electronic parts, namely, semiconductor wafers. Prior to the invention of Uehara, plasma treatment of electronic parts was performed in batch-wise fashion. As Uehara describes, such simultaneous plasma treatment of a large number of parts generally does not result in an even reaction (i.e., etching or cleaning) at the surface of a substrate. Batch-wise treatment also reduces productivity by interrupting the flow of processing and assembly of parts.
Uehara provides for a reaction chamber having an open bottom portion and a wafer "table" that moves vertically up and down to be vacuum-sealable with the opening of the reaction chamber. The apparatus furlier includes an in-take carrier means for carrying a wafer to a position adjacent the wafer table, and an in-take pick-up means for picking up the wafer from the in-take carrier means and placing the wafer onto the wafer table. Disclosed in the patent are two combinations of such in-take carrier and pick-up means, one of which employs two revolving arms, each having a suction type pick-up, the other of which employs two linear traveling arms, each having a suction pick-up as well. After the single wafer has been placed on the wafer table, the wafer table is raised to seal against the reaction chamber and the plasma process is initiated. Out-take means identical to the in-take carrier and pick-up means are used for removal of the treated wafer from the wafer table after the wafer table has been disengaged and lowered from the reaction chamber opening.
The invention of Uehara offers substantial advantages in that it makes possible the in-line, hands-off plasma processing of individual parts (wafers). However, both of the embodiments disclosed are much more limiting in their scope of operation than is desirable. The invention does not allow, when it is desired, for the plasma treatment of more than one part at a time. It was noted previously that individual processing of parts is advantageous with respect to the evenness of the plasma reaction that may be obtained. However, it is also the case that a sufficiently uniform reaction may be obtained, depending on the nature of the parts (and upon appropriate spacing therebetween), where more than one part at a time is treated. Uehara does not address this issue. In addition, pick-up mechanisms of the type shown in Uehara, which as noted is in the form of a suction device, are known to be not entirely free from droppage and breakage of parts due to temporary loss or irregularity of vacuum pressure.
Shown in U.S. Pat. No. 4,318,767, issued to Hijikata et al. on Mar. 9, 1982, is another automatic in-line plasma system for treatment of semiconductor wafers. Hijikata employs a non-movable reaction chamber with a vertically movable wafer table contained therein. Shutter-like slits, which are vacuum-sealable and which are present at opposing ends of the reaction chamber, provide entry and exit portals for the wafers. The wafers are introduced into the reaction chamber with a pair of slidable parallel arms spaceably distanced so as to support a wafer therebetween. In the process sequence, a single wafer is loaded onto the ends of the arms via a conveyor belt apparatus. The arms then slide forward to extend into the reaction chamber through the entry portal such that the wafer is positioned over the wafer table. The wafer table moves upward to a height just above the arms, lifting the wafer off of the arms in the process. After the arms have been retracted, the entry slit is sealed, the chamber evacuated, and the plasma process initiated to treat the wafer lying on the table. The wafer is removed by extension through the exit portal of a pair of arms identical to the ones previously employed followed by a lowering of the wafer table, which causes the treated wafer to rest upon the arms. Retraction of the arms then removes the wafer from the chamber.
Hijikata eliminates the precarious suction pick-up arrangement of Uehara, but again fails to offer an option for treating more than one part at a time in an in-line fashion. Nor is the invention of Hijikata amenable to such, since even were more than one part crudely loaded onto the ends of the sliding arms of the apparatus, no mechanism is available for properly spacing the parts upon the wafer table, such spacing being critical when more than one part is subjected to plasma treatment.
U.S. Pat. No. 4,889,609 to Cannella discloses an automated dry etching system which is titled "Continuous" but utilizes input and output belts which are enclosed in pressurized chambers which are maintained at a preselected partial vacuum. The enclosed nature of these chambers necessarily limit the number of parts that can be treated before the chambers have to be opened for loading a new batch to be processed. Additionally, the configuration of the input gate allows a very limited number of parts to be treated at once, and consequentially, the throughput of this system can be expected to be likewise limited.
U.S. Pat. No. 4,252,595 to Yamamoto et al. illustrates a plasma etching apparatus which includes a rotatable disk in the etching chamber, or alternately, a conveyer assembly, which is also included within the plasma chamber. Both of these variations can be expected to have problems related to the use of moving parts within the plasma chamber. Moving parts typically require lubricants, which can, over time, contaminate the etching chamber and the treated parts. Especially in near vacuum conditions, out-gasing of lubricants can be expected, and effects of even minute amounts of contaminants can be cumulative over time. Additionally, when moving parts are exposed to conditions such as in a plasma etching chamber, these parts are susceptible to corrosion. Moving parts which operate on fine tolerances can be expected to require frequent replacement when exposed to such harsh operating conditions.
U.S. Pat. No. 5,587,205 to Saito et al. also shows a plasma processing method including an electrode stage on a liffing mechanism. These moving parts can be expected to experience the same difficulties of contamination and corrosion discussed above. Additionally, the throughput of the system would appear to be very limited.
U.S. Pat. No. 4,405,435 to Tateishi et al. discloses a plasma treatment apparatus, but there is an elevator in the etching chamber, thus introducing moving parts. Once again, these moving parts can be expected to experience the same difficulties of contamination and corrosion discussed above.
Because of the limitations associated with most presently available plasma treatment systems, a substantial need still exists for such a system as offers improved processing capability while also providing for the simultaneous treatment of a plurality of parts.